Bit of a different one! I originally wanted to create a classic theme for the entirety of youtube, however I recently gained access to the yt2009 frontend closed beta. After playing around with it for around a month, I realized there is no need to use youtube.com ever again. It is that accurate, and has several other goodies which will make it really neat when it releases for real. Unfortunately, as it is a frontend, there is no way to upload videos from it. Therefore I found it a fun challenge to eliminate the need to use the actual Youtube.com to upload videos (Though I should say this will also work on normal Youtube).
If you have access to the beta you should install the Redirector Chrome extension to get it to function properly, and set two redirects. First redirect (closed beta url)/my_videos_upload to https://youtube.com/upload. Second redirect the url for your uploaded videos page back to the homepage of yt2009. There you go, you should have it all set up to kind of be like 2009. Now I believe the only modern page left to change is the "Sign In" page if anyone is up to the challenge of that (I might be).
The theme can be located here: https://userstyles.world/style/8127/youtube-uploader-classic-primarily-for-use-with-upcoming-yt2009-frontend